This invention relates generally to a method of making a composite material.
A composite material is constructed by assembling an arrangement of reinforcing fibers, then encapsulating or embedding the fiber arrangement in a binder or “matrix” material. Such composite materials have application as ballistic articles such as bulletproof vests, helmets, and structural members of military and law enforcement vehicles, as well as briefcases, raincoats, parachutes, umbrellas, and other items. Fibers conventionally used include aramid fibers, graphite fibers, nylon fibers, ceramic fibers, glass fibers, and the like.
It is known in the art to construct the building blocks for impact resistant composites—known as prepreg layers—by bonding or laminating together individual layers of unidirectional coplanar fibers that have been impregnated with a matrix material. Generally, the individual fibers are impregnated with the matrix material by immersing them in a bath or film of the matrix material before forming each prepreg layer so that the individual strands within each layer have sufficient structural integrity to remain coplanar. It is also known in the art to orient adjacent unidirectional fiber layers non-parallel to one another to increase the structural integrity of the prepreg layers.
A problem with these known techniques is that a large amount of matrix material must be used to create the composite material, which increases both the assembled weight and the cost of creating the composite material. Prior art methods for constructing a composite material have taught away from assembling multiple adjacent layers of unidirectional fibers without first treating the individual fibers and/or fiber layers with a matrix component. These prior art references have reasoned that the distribution of the fiber layers will be disordered by the impregnation process if matrix material is not already present on the individual fibers or fiber layers, hence causing technical issues such as the occurrence of sink marks due to differences in fiber volume fractions, and thereby damaging the structural integrity of the composite material. Furthermore, as noted above, the prior art has reasoned that impregnating the individual strands before forming them into prepreg layers is necessary to give the individual strands sufficient structural integrity to remain coplanar within each layer.
Hence, an improved method is needed for constructing a composite material that minimizes the amount of matrix component that is required to impregnate the fiber arrangement, while not diminishing the performance characteristics of the constructed composite sheet.
Relevant prior art patents include U.S. Pat. No. 5,112,667, U.S. Pat. No. 5,480,706, and U.S. Pat. No. 5,874,152.